1. Field of the Invention
The present invention relates to a liquid crystal display device which includes a backlight for illuminating a liquid crystal panel (for displaying images) from behind and executes brightness adjustment of the backlight in response to an image signal inputted for the displaying of the images. The present invention relates also to a control method for the backlight.
2. Description of the Related Art
A liquid crystal display device is equipped with a non-emitting liquid crystal panel (light-transmissive optical modulation element) and a backlight arranged behind the liquid crystal panel to illuminate the panel with light, differently from self-emission display devices (CRT (Cathode Ray Tube), plasma display panel, etc.). In general, the liquid crystal display device displays images at desired brightness by controlling the optical transmittance of the liquid crystal panel according to the brightness specified by the image signal while making the backlight's light source (e.g., LED) emit light at a fixed brightness level irrespective of the image signal. Therefore, the electric power consumption of the backlight remains constant without decreasing even when dark images are displayed. This leads to low electric power efficiency of the liquid crystal display device. As a countermeasure against this problem, a well-known technique employs variable brightness of the backlight and reduces the electric power consumption by controlling the grayscale level of the liquid crystal panel and the brightness of the backlight according to the brightness level (luminance level) of the inputted image signal. There also exists a technique known as “area control” or “local dimming”, in which the backlight is segmented into multiple areas and the backlight brightness control is conducted for each of the areas.
For example, an image display device disclosed in JP-A-2006-30588, aiming to provide a high-performance ACC (Automatic Contrast Circuit) by controlling the LED backlight brightness in units of pixels, comprises screen information analyzing means which detects average brightness information on the image signal, black level areas and white level areas, and LED backlight control means which controls the brightness of each LED backlight according to a control signal outputted by the screen information analyzing means.